Intramedullary Nail

ABSTRACT

A versatile intramedullary nail is constructed in two cooperating and optionally interlocking pieces, with a further optional annular restoration hub. The two cooperating pieces, when interlocked, approximate a long shaft, generally tubular in cross-section, with a recessed area on the male piece adapted to receive the annular restoration hub. The female piece is adapted to receive the flange of the male piece coaxially, and—unless a locking screw or bolt is inserted through the flange—the two pieces can rotate axially. Alternatively, the nail can be constructed of a single solid piece.

BACKGROUND AND CROSS REFERENCE

1. Field of the Invention

The present invention is a versatile nail for use in the intramedullarycanal of the ulna or the fibula, and claims priority to U.S. PatentApplication Ser. No. 62/036,426 filed 12 Aug. 2014 and No. 62/039,275filed 19 Aug. 2014, each of which is incorporated herein by reference.

2. Description of Related Art

Intramedullary nails are known in the art, and are widely usedthroughout the world to repair fractures or to reinforce bone shaftsduring and after surgery of various types. The intramedullary canal(synonymous with the marrow canal) is an ideal place for insertion of asupport structure, because the relatively softer bone or marrow providesan easy implantation site, and intramedullary implants are lesscompromising to bone than other bone inserts. Traditional intramedullarynails or rods have typically been secured with locking bolts or screwsto the adjacent bone, to prevent unwanted rotation, and a customary“cloverleaf” cross-sectional shape also prevents unwanted rotation ofimplants within the intramedullary canal.

One disadvantage of a traditional intramedullary nail inhered in itselongated length: surgical implantation was often complicated simply bythe sheer size of the nail. Also, prior art intramedullary nails androds were typically designed to be completely stationary within thebone, and hold the bone immobile-specifically not allowing motion withinthe bone but only at the adjacent joint. This invention is specificallydesigned to allow motion wihin a long bone in a controlled fashion,while providing stability in all planes and provide load sharing.Additionally the device may enable immediate rehabilitation to beginwithout the need for a period of immobilization to allow soft tissues toheal completely.

For example, during prior art distal radia-ulna joint fusion proceduresintended to reduce pain due to arthritis or other deterioration,sometimes an osteotomy along the ulna was performed to restore range ofmotion otherwise lost by fusing the distal radia-ulna joint. However,having the ulna in two pieces, with only one end of each piece's beingsecurely anchored, created problems of its own such as instability ofthe proximal ulna stump, even though the osteotomy did restore somerange of motion after the fusion. A stationary intramedullary nail wouldhave merely removed the range of motion restored by the ulna osteotomy.A need therefore remains for a versatile intramedullary nail which notonly provides the traditional reinforcement function of a prior artintramedullary nail or rod, but also can restore range of motion to oneor more joints adjacent to the implant, as needed.

SUMMARY OF THE INVENTION

In order to meet this need, the present invention is a versatileintramedullary nail constructed in one piece or in two cooperating andoptionally interlocking pieces, with a further optional truncatedannular restoration hub. The two cooperating pieces, when interlocked,approximate a long shaft, generally tubular in cross-section, with arecessed area on the male piece adapted to receive the truncated annularrestoration hub. The female piece is adapted to receive the flange ofthe male piece coaxially, and—unless a locking screw or bolt is insertedthrough the flange—the two pieces can rotate axially and independentlyof each other. (Alternatively, the aforesaid nail structures can bemanufactured as a single piece and, in such case, no interior rotationwill take place.) Bolt or screw holes near the ends of either pieceallow selective anchoring of either or both pieces to the adjacentintramedullary bone. However, if the interconnected pieces areinterlocked and only one piece is bolted or screwed to the adjacentintramedullary bone, the other piece can rotate freely within theintramedullary canal to restore range of motion to an adjacent joint.Conversely, if the interconnected pieces are each bolted or screwed totheir respective bone but the interconnection is NOT interlocked, thenthe two pieces maintain their lengthwise rigidity but can rotate axiallydepending on exertion from an adjacent joint. The present intramedullarynail or plate is particularly suited for use within the ulna or fibula,especially after wrist or even ankle joint fusion creates a need forimproved range of motion in the hand or foot.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of the intramedullary nail of the presentinvention, shown without the restoration hub.

FIG. 2 is a plan view of the intramedullary nail of FIG. 1.

FIG. 3 is a side sectional view of the intramedullary nail of FIG. 1.

FIG. 4 is a partial plan view of the intramedullary nail of FIG. 1,shown with the restoration hub in place; and

FIG. 5 is a perspective view of the intramedullary nail and restorationhub of FIG. 4, inverted 180 degrees to show the anchor holes in therestoration hub.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a versatile intramedullary nail constructed inone piece or in two cooperating and optionally interlocking pieces, witha further optional truncated annular restoration hub. The twocooperating pieces, when interlocked, approximate a long shaft,generally tubular in cross-section, with a recessed area on the malepiece adapted to receive the truncated annular restoration hub. Thefemale piece is adapted to receive the flange of the male piececoaxially, and—unless a locking screw or bolt is inserted through theflange—the two pieces can rotate axially and independently of eachother. (Alternatively, the aforesaid nail structures can be manufacturedas a single piece and, in such case, no interior rotation will takeplace.) Bolt or screw holes near the ends of either piece allowselective anchoring of either or both pieces to the adjacentintramedullary bone. When both pieces of the nail are anchored (via boltor screw) to the adjacent bone, the two pieces can rotate axially due tothe configuration by which the two shafts cooperate. However, if theinterconnected pieces are interlocked and only one piece is bolted orscrewed to the adjacent intramedullary bone, the other piece can rotatefreely within the intramedullary canal itself, to restore range ofmotion to an adjacent joint via relative axial rotation between twoportions of the same bone. The present intramedullary nail isparticularly suited for use within the ulna or fibula, especially afterwrist or even ankle joint fusion creates a need for improved range ofmotion in the wrist or ankle.

Referring now to FIG. 1, an intramedullary nail according to the presentinvention is shown in perspective view. The intramedullary nail 10contains two portions, namely, the distal stem 12 (having a distal stemend 14 which is typically but not necessarily smoothly curved) and thefree proximal stem 24 having a free proximal stem end 32 (also generallysmoothly curved). The distal stem 12 and the proximal stem 24 areconstructed as a single piece with a hub core 18. The hub core 18 hasless width than the diameter of the distal stem 12 and typically hassmooth rectangular sides as shown in FIG. 1. The distal stem 12 containsdistal stem anchor holes 16 and the hub core 18 contains hub core anchorholes 20. The free proximal stem 24 contains stem anchor holes 30 and alocking hole 28. As is the case throughout this specification, anchorholes may be either holes for bolts or threaded holes for screws-thepurpose of the anchor hole is a recess or void adapted to receive afastening device suitable for interconnecting the intramedullary nail toadjacent bone. The free proximal stem also contains an axial hingeanchor hole 28, explained further below.

Referring now to FIG. 2, the same structures of FIG. 1 may be seen inplan view, and in FIG. 3 not only does it become apparent that the hubcore 18 is inset (with respect to its distal stem) only on three sides,but that there is an axial hinge post 22 on the distal stem 12. FIG. 3also shows the axial hinge receptacle 26 in the free proximal stem 24,which receptacle is cylindrical and only slightly larger than thecylindrical axial hinge post 22. The concentric cooperation of the axialhinge post 22 within the axial hinge receptacle 26 means that the distalstem 12 and the free proximal stem 24 can rotate freely about eachothers' axes except when a bolt or screw (not shown) is present in theaxial hinge anchor hole 28. By the way, the reason the free proximalstem 24 is called “free” is not that it cannot be anchored as desired,but because it is “free” of the hub core present on the other piece ofthe intramedullary nail. Incidentally, and as is explained elsewhere inthis patent application, the “free proximal stem” is sometimes leftunanchored within its intramedullary canal, so as to be able to rotatetherein, but an unanchored distal stem can also rotate within theintramedullary canal, so “free” in “free proximal stem” should not beassumed to mean rotatable, per se.

When the present intramedullary nail is used to restore an ulnaosteotomy (such as has been performed in the past to restore range ofmotion lost to distal radia-ulna joint fusion) in order to implant thepresent intramedullary nail it is customary for a portion of the shaftof the ulna to be removed-anywhere from about 10 to 20 millimeters ofbone or so. Removal of a portion of the bone greatly facilitations theimplantation of the intramedullary nail pieces at the cut ends of thebone. However, the present intramedullary nail is by definition narrowerthan the bone into which it is implanted, because the implant must fitin the intramedullary canal inside the bone. Therefore, theintramedullary nail, being smaller in diameter than the bone diameter,does not completely fill the excised 10 to 20 millimeter bonesegment—and providing that filling function is the purpose of therestoration hub capsule 34 shown in FIG. 4. The restoration hub capsule34 is designed to be longer than the length dimension of the hub core18, with interior diameters designed to match the shape and position ofthe hub core 18 (see restoration hub capsule interior flange 36) and thelarger diameters of the distal stem and free proximal stem. In otherwords, as shown in FIG. 4 the interior diameter of the restoration hubcapsule 34 is designed to mate both with the hub core 18 and with thelarger-diameter exterior of the distal stem 12 or the free proximal stem24. FIG. 5 shows the assembly of FIG. 4 inverted by 180 degrees, to showthe restoration hub capsule anchor holes 38. The restoration hub capsuleanchor holes 38 may be used to fasten (via one or two bolts or screws)the restoration hub capsule to the two-part intramedullary nail. The useof the restoration hub capsule is optional. The present invention willwork without the restoration hub capsule. In an ulna implantation,however, the restoration hub capsule keeps the patient from probing andfeeling—or even seeing—an indentation in the ulna and thus in theforearm, were the restoration hub capsule not in position. Imaginetouching a forearm with the hand-without the restoration hub capsule,one would feel sharp ridges through the skin, about a third of the wayup the forearm from the wrist, and such ridges would lead to greatpatient dissatisfaction. An additional benefit of the optionalrestoration hub capsule is minimizing longitudinal pistoning when thenail is inserted with one side not locked as previously described whenused to restore forearm rotation after distal radius and ulna fusion.

In operation, the structures of FIGS. 1-5 provide the maximumversatility to the surgeon as is possible. If the distal stem 12 and thefree proximal stem 24 are simply adjoined by bolt or screw via axialhinge anchor hole 28, the present invention functions as though it werea single piece intramedullary canal implant, whether further anchoredwith additional bolts or screws or not. Given the immediately previouslydescribed configuration of distal stem 12 and free proximal stem 24affixed at the axial hinge anchor hole, if either but not both of thedistal stem 12 or the free proximal stem 24 is affixed to its adjacentbone, the other stem will be able to rotate freely within its respectiveintramedullary canal as long as the axial hinge post and the axial hingereceptacle remain affixed together. However, even if both the distalstem 12 and the free proximal stem 24 are affixed to their adjacentbones via their respective anchor holes, as long as the axial hinge post22 is left free to rotate within the axial hinge receptacle 26 (that is,there is no screw or bolt in axial hinge anchor hole 28) then the twopieces will be able to rotate axially. In an ulna restoration incidentto wrist fusion, such axial rotation restores range of motion to thewrist and forearm as a result of one part of the ulna's being able torotate axially vis a vis the other part.

Variations on the above combinations will be apparent to orthopedicsurgeons accustomed to bone implants. For example, even though manyanchor holes are provided in pairs (not the axial hinge anchor hole forobvious reasons), only one of the anchor holes needs to be used at atime, depending on accessibility issues and choice of bone for fixation.FIG. 3 shows screw threads within the anchor holes because threadedscrew fasteners are generally better suited to the invention than truebolts, which would typically require a complete through hole withaccompanying nut. Materials used to construct the pieces of theintramedullary nail shown in FIG. 1-5 are any materials-generallymetals-suitable to bone implants within an animal or human subject, andsuch materials are well known in the art. However, in order to minimizefriction during rotation, the interface between the axial hinge post 22and the axial hinge receptacl 26 may be coated with a biocompatiblecomposite material such as PEEK (polyaryletherketone) or UHMWPE (ultahigh molecular weight polyethylene). Whereas a clear indication for thepresent intramedullary nail is the ulna, it is also suitable for use inthe fibula and-because it is so versatile-the instant intramedullarynail can really be used in any desired intramedullary canal in which thesurgeon wishes to add reinforcement to the bone. If desired, theintramedullary nail can be constructed with the axial hinge receptacle'sbeing located in the distal stem rather than in the free proximal stem,but optimally the axial hinge receptacle is in the free proximal stembecause the larger diameter of the free proximal stem provides greaterstructural stability despite the weakening void presence of the axialhinge receptacle.

Although the invention has been described as a two-piece deviceconsisting of a distal and a proximal stem, another one-pieceimplementation is possible. FIG. 1 may be viewed as a one-piece device.The implanting procedure for the one piece-device is different from thetwo piece device. The one piece-device can accept a restoration hub atthe hub core 18. The one piece implementation can function as aconventional intramedullary nail to reinforce the host bone when bothends are fixated to their respective adjacent bones. If only one end isfixated to its adjacent bone and the other end is not fixated but leftfree to rotate within the interamedullary canal, the device functions asan axial hinge. Furthermore, although the invention has been describedwith particularity above, with specific reference to structures,conformations, and functions, the invention is only to be limitedinsofar as is set forth in the accompanying claims.

1. A two-piece intramedullary nail having a first piece and a secondpiece, wherein at least one piece has a curved end surface and furtherwherein said first piece bears an axial hinge post which concentricallyengages an axial hinge receptacle in said second piece, and furtherwherein each of said first piece and said second piece have at least oneanchor hole therein.
 2. The two-piece intramedullary nail according toclaim 1, wherein said second piece has an anchor which extends into andthrough said axial hinge receptacle.
 3. The two-piece intramedullarynail according to claim 1, wherein said first piece has a hub corecomprising a narrower shaft portion adjacent said axial hinge post. 4.The two piece intramedullary nail according to claim 3, wherein said hubcore contains two-hub core anchor holes.
 5. The two-piece intramedullarynail according to claim 4 wherein said first piece is a distal stembearing two distal stem anchor holes and said second piece is a freeproximal stem bearing two free proximal stem anchor holes in addition tosaid axial hinge anchor hole.
 6. The two-piece intramedullary nailaccording to claim 5 wherein a third piece comprising a restoration hubcapsule is placed over said hub core.
 7. The two-piece intramedullarynail according to claim 6 wherein said restoration hub capsule containsat least one restoration hub capsule anchor hole.
 8. The two-pieceintramedullary nail according to claim 7 wherein said restoration hubcapsule has two interior diameters to match the dimensions of saiddistal stem and said hub core.
 9. A single-piece intramedullary nailwherein said nail has at least one curved end surface and furtherwherein either or both ends bears at least one anchor hole therein,wherein in operation said nail may be anchored only at one end so as torotate axially within the bone at said at least one curved end.